Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

758
FXUS63 KLOT 052307
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
607 PM CDT Tue May 5 2026

.KEY MESSAGES...

- Additional showers late this afternoon and evening mainly well
  south of I-80.

- Small chance for some spotty showers Thursday, better chances
  on Friday.

- Moderating temperatures through the end of the week and into
  Saturday.

&&

.DISCUSSION...
Issued at 1240 PM CDT Tue May 5 2026

A secondary impulse, attendant increase in upper-level jet
divergence, and enhanced mid-level f-gen will result in another
increase in showers south of I-80 this afternoon and evening.
Any MUCAPE will be relegated well to the south across parts of
central and downstate Illinois, so no thunder mention appears
necessary in the gridded forecast. With activity expected to
diminish overnight, there is some potential for a little shallow
fog development along a diffuse confluence axis south/southeast
of the Kankakee River. Low confidence in sufficient clearing,
combined with a lack of a deeper near-surface hydrolapse
precludes any fog addition at this time, however. Finally,
temperatures may meander into the low/mid 30s across interior
northern Illinois tonight. Given mixed-out dewpoints this
afternoon, have not added a frost mention at this time.

Forecast guidance (including the NAM) depicts deep boundary
layer mixing developing on Wednesday. Have nudged winds/gusts
up a bit with mean boundary layer flow progged to be in the
15-20 kt range, and commensurately nudged afternoon dewpoints
down closer to some of the more well-mixed guidance (HRRR/RAP).
Given the stronger flow, it seems like any lake breeze should
end up tied pretty close to the Illinois shore, with somewhat
deeper inland movement across Lake/Porter counties.

High pressure will build in just to our south Wednesday night.
It looks like some mid and high cloud cover will be present
over the region, although this may end up being somewhat
brief/ephemeral. With the pressure gradient relaxing overnight,
looks like there`s a potential for temperatures to drop pretty
quickly through the evening. Have introduced some patchy frost
mention in the grids with the expectation of dewpoints slowly
recovering overnight. If cloud cover doesn`t end up impeding OLR
too much, temperatures could drop near/below freezing on a
localized basis.

Thursday will feature another day with deep boundary layer
mixing, and forecast guidance event depicts the development of
a little surface-based instability during peak heating. A series
of sheared-out mid-level perturbations are also forecast to
drift across the region during the afternoon and evening,
pushing a seasonably cool 500 mb airmass (mid -20s C) overhead.
Could envision some isolated/spotty high-based shower development
during the afternoon as a result.

Somewhat deeper moisture and more coherent synoptic scale
forcing will arrive on Friday, resulting in another period of
mainly light shower activity, potentially lingering into Friday
evening. The next shortwave trough looks to be fast on the heels
of Friday`s with warm air advection in advance of the next wave
looking to provide milder temperatures Saturday. That will be
followed by another chance of showers Sat night with a frontal
passage, followed by a return to cooler temps Sunday into
Monday.

Carlaw/Izzi

&&

.AVIATION /00Z TAFS THROUGH 06Z THURSDAY/...
Issued at 607 PM CDT Tue May 5 2026

There are no significant aviation weather concerns anticipated
through the period. VFR conditions will prevail through the
period, with only some higher high CIGs at times. Otherwise,
winds will abate below 10 kt early this evening and may even
trend more towards an easterly direction for a few hours before
turning back northerly later this evening and overnight. Winds
will then favor a northwesterly direction during the day
Wednesday, with some occasional gustiness up around 20 kt
expected in the afternoon.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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